From the prior art several devices and methods are known, in order to coat surfaces of panel-shaped components. From the WO 2009/074174 A1 of the same applicant for instance a coating device is known, wherein a liquid coating material is transferred by means of an application drum to an application belt. Then, the application belt is pressed by means of a pressure drum onto the panel-shaped components to be coated in order to transfer the liquid coating material from the coating belts to the surface of the components to be coated. Therefore, the panel-shaped components are guided via a transport belt together with the coating belts through the device. It is a disadvantage of such drum-based application methods that the transferred coating comprises a wave-shaped surface due to the curvature of the application drum, wherein it does not matter whether the coating material is dispensed directly from the drum onto the surface to be coated or indirectly via the coating belt. However, the mountains and the valleys of this wave-shaped surface are so small that surfaces, which are manufactured by that method, are commonly able to be printed with a common 3-color-print very well. However, it has been shown that this wave-shaped surface structure is disadvantageous for digital print methods. It is assumed, that the unevenness of surfaces, which are coated in that manner, even if the unevenness is very small, may possibly lead to a sub-optimal print image for the digital print due to electric potential differences.
From the prior art also coating methods are known, which work without revolving drums. In particular, so called curtain-coating methods are known, wherein a liquid curtain of coating material is generated, through which the components to be coated are guided. The curtain of liquid coating material may for instance leave from a dispenser and may fall down freely due to gravity. Also dispensers are known, wherein the liquid curtain is actively outputted via nozzles.
A typical representative of such a curtain-coating is for instance described in the EP 1 252 937 A1. Herein, in FIG. 1 of this document, a schematic diagram of a device for the curtain-coating is shown. The panel-shaped components are guided via an input transport device through the liquid curtain of coating material and are guided away via an output transport device. Input and output transport devices comprise herein revolving transport belts. In curtain-coating devices for the coating of discrete components, like for instance panel-shaped components, a gap has to be imperatively provided between the input transport device and the output transport device, through which the liquid curtain may fall in order to lead surplus coating material away. This is caused by the fact that during the coating of panel-shaped components unavoidably more or less large gaps exist between two succeeding components.
Contrary to that, also curtain-coating devices are known, which are designed for the coating of sheet material, like for instance for the coating of paper sheets. In these devices, commonly no gap is necessary since the sheet to be coated does not comprise any interruption and is so to say “endless”, when it is guided through the coating curtain.
Although the common devices and methods for the curtain-coating work sufficiently, there is still a need for improvements. It has been in particular shown that the coating of (slightly) curved panel-shaped components is problematic, since they will be coated during the guidance through the curtain at their raised areas in another way than at the relatively low areas. This comes in particular up for components, which comprise a specific flexibility, like for instance large but thin panels made of wood material. It may in particular come up that the liquid curtain of coating material breaks at an end section of a panel, which is guided through the curtain, when this end section is bent downwards. Moreover, there is the risk that the front section of a panel, which is guided through the curtain, gets a hit during the contact with the output transport device, when the front section is bent downwards. Hereby, the coating process is disturbed. These problems arise more often for relatively thin panel-shaped components, i.e. components, which comprise a large length relative to their thickness and which comprise accordingly a specific flexibility.
Based on the above mentioned prior art, the problem arises to provide a device and a method for the curtain-coating of panel-shaped components, by which the above mentioned disadvantages of the prior art may be eliminated and respectively reduced. In particular there is the problem to provide a device and a method, by which thin panel-shaped components and respectively uneven panel-shaped components may be coated in good quality with a liquid coating-curtain. In particular, a homogeneous coating of panels made of wood material may be allowed by the present invention, wherein the panels comprise a slight convex curvature over their length.
These and other problems, which are mentioned during the reading of the following description or which may be recognized by the person skilled in the art, are solved by a device for the curtain-coating according to claim 1 and by a method according to claim 14.